Sessions Westminster A mantel clock Part II – Dis-assembly

This is Part II of a multi part series on the Sessions Westminster A chiming mantel clock.

Side view of Sessions Westminister A
Side view of Sessions Westminster A

Inside the plates they are a conventional Sessions clock. Outside the plates is an entirely different story

Sessions Westminster A clocks are true chiming clocks that play the Westminster chime sequences on the quarter hours and strike the hour count on the hour. The unique design combines the chiming and striking functions in one train powered by a single main spring. Between the movement plates these movements are very similar to other Sessions non-chime (strike only) movements. The going (time) train is controlled by a basic recoil escapement with the strip pallets or verge located between the plates. Inside the plates they are a conventional Sessions clock.

Outside the plates is an entirely different story. At the front of the movement one will notice that this is a rack and snail strike train but it has TWO racks and TWO snails. A look at the back of the movement reveals a small cam in the middle of the plate and a large “player drum” or pin drum. The two racks working together with the little cam and the player drum, which can shift outward to play chimes or inward to strike the hour, is what makes it all work. The chime sequence is self‐synchronizing and with so few working parts, once setup correctly this can be a relatively trouble free movement. (Source R. Croswell’s Taming the Sessions Two Train Clock)

This clock requires servicing for two reasons;

  1. It runs for several minutes or an hour or so and then stops
  2. The striking and chiming is very erratic. It might strike 4 o’clock one hour and 9 o’clock the next and the hammers “hang up” during the quarter hour chime.

There are a number of “exterior” parts that must be removed before separating the plates

Dis-assembly of the Westminster A is conventional however there are a number of “exterior” parts that must be removed before separating the plates. The regulator gearing, verge, drum assembly, hammers and racks as well as other parts are removed one after another. The additional parts add considerable complication to the movement and can lead to issues when servicing. I will describe two particular issues I have encountered in the process of working with this movement. I believe these issues, which I will describe later, are likely what frustrate most clock repair persons when working on the Westminster A.

Rear plate
Rear plate showing regulator, verge and chime drum. Clamp on mainspring

I chose to leave the mainsprings in while taking the movement apart though I contained the power using C-clamps. On this clock the mainsprings can be removed without dis-assembly. This allows the repair person to easily service the mainsprings or the clicks (which are notoriously bad on Sessions clocks generally).

Unfastening the drum and hammer assembly went without issue since there are only two bolts securing it to the plate.

The 2 racks, a unique feature, work together to produce the strike. They are located one on top of the other and are secured to a post.

Two racks stacked on top of each other
Two racks stacked on top of each other. The post on the right accommodates two springs

Taking them off requires releasing a pressure washer on the top of the post. They came out easily. However, one rack is missing a return spring which might partly explain the erratic striking of the clock. Such a simple thing that may make a big difference. I may have to buy or fashion a spring.

Rack with spring
Rack with spring
Rack without spring
Rack without spring. The spring clips into the hole on the rack arm

Specialized tools are needed to remove some parts. Those I don’t have

Two issues.

One, I could not remove the hub supporting the gathering pallet pins seen here. It’s unfortunate because there is more lateral movement of the arbour that I am comfortable with which tells me that a bushing is required. I did not want to risk damaging the arbour and I don’t have specialized tools to do the job. I may have to live with it. However, it may not be so bad once the other bushing work is completed.

Gathering pallet pins
Gathering pallet pins

Two, I could not remove the centre cam despite pulling and gently prying.

Centre shaft cam
Centre shaft cam

Again, I did not want to risk damaging the arbour. Specialized tools, such as a puller in this case, are required to remove it. That, I don’t have.

This clock has a unfortunate reputation for soft pivots

I will have to work around these two issues. Pressure fitted parts on any movement are very frustrating when said parts cannot be removed without special tools and this one is a challenge indeed. Re–assembly might be a little frustrating particularly with the centre arbour still attached to the rear plate which may effectively be “in the way” of positioning other wheels in place.

I inspected the pivots on the wheels and they all look good (no tapering) with expected wear for a clock of this period. I was worried because this clock has a reputation for soft pivots and perhaps because this is a later model, Sessions might have been introduced harder steel for the pivots. There is plenty of bushing work that needs to be done, however.

On to cleaning, bushing work, re-assembly and testing in Part III.

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